Centralized traffic controlling system for railroads



Aug. 24, 1937. N. D. I RESTON El AL CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS 5 Sheets-Sheet 1 Filed April 14, 1953 MUELO QOQFZOU INVENTORS ND. Preston and TJ. Jud

BY M THMTOIQNEY Aug. 24, 1937.

N. D. PRESTON ET AL Filed April 14, 1935 INVENTORS NDPreston and TJJqd BY a THEIR 'kORNEY Aug. 24, 1937. N. D. PRESTON El AL CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed April 14, 1935 5 Sheets-Sheet 3 *2 a N2 H mm mm INVENTORS Aug. 24, 193 7.

N. D. PR ESTON ET AL 2,090,917

CENTRALIZED ITRAFFIC CONTROLLING SYSTEM FOR RAILROADS 5 Sheets-Sheet 4 m3 m2 wx lt 35 N9 mam NE .W w 1% ET' 3Q A $6: mAN 4 m QNMHTIT RNWT 0mm mmm $2 Filed April 14. 1933 THEI ATTORN.EY

g- 1937. N. D. PRESTON ET AL CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS 5 Sheets-Sheet 5 Filed April 14, 1933 .mflwei 8 g m N T M w a m n m H D. H Dm T N Patented Aug. 24, 1937 UNETED STATES CENTRALIZED' TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Neil D. Preston and Thomas J. Judge, Rochester,

N. Y., assignors to General Railway Signal Company, Rochester, N. Y.

Application April 14, 1933, Serial No. 666,182

23 Claims.

This invention relates to centralized traffic controlling systems for railroads, and more particularly pertains to the communication part of such systems.

By means of the centralized trafiic controlling system contemplated by the present invention, the switches and signals at field stations along a railroad system are placed under the supervision of an operator at a control office and the condition of such switches and signals, together with various other trafic conditions, are transmitted to the control oflice to provide the operator with such information as may be necessary for the proper governing of train movements.

The present invention more particularly relates to a centralized traffic controlling system, Wherein the supervision of the trafiic governing devices and the indication of their conditions is accomplished over a communication system having only two line wires. These two line wires serve to connect the control ofiice with each of the field stations.

The apparatus at the control office and at each field station is organized to be responsive to different series of impulses applied to the two line wires and arranged in distinctive combinations, in accordance with the character of the messages desired to be transmitted and in accordance with the station to or from which such messages are to be transmitted. Each of these series of impulses causes the apparatus at the control office and at the field stations to operate through what is termed a cycle of operations.

More specifically, a battery or other suitable source of current is located at the control office and also another similar source of current is located at the last field station of the system. Thus, the operator may cause the transmission of a series of positive and negative impulses in various combinations from the source located in the control ofiice to accomplish what is termed a control cycle of operations. Likewise, any field station may automatically cause the transmission of a series of positive and negative impulses in various combinations from the source located at the end field station to accomplish what is termed an indication cycle of operations.

The impulses transmitted from the control office are of substantially equal duration and are separated by substantially equal time spaces, while the impulses transmitted from a field station are made long or short in various combinations, being separated by substantially equal time spaces.

Step-by-step means located at the control office and at each field station operate in response to the application of impulses irrespective of their character. During a control cycle one of two distinctive messages or controls may be transmitted on each step by reason of the distinctive character (polarity) of the corresponding impulse appliedto the line circuit. During an indication cycle choices of four distinctive messages or indications may be transmitted on each step by reason of the distinctive character (polarity and duration) of the corresponding impulse applied to the line circuit. In other words,

it is possible to transmit controls with a choice of two on each step of a control cycle and to transmit indications With a selection of either one choice of four or two choices of two each, on each step of an indication cycle.

Other feaures of novelty embodied in the present invention reside in the manner in which the sides in the manner in which the timing characteristics are determined in a'positive and direct manner. 1

These characteristic features of the present invention, thus briefly stated, will be explained more in detail in the following description of one embodiment of the invention and various other characteristic features, functions and advantages of a system embodying this invention will be in part pointedfout'and inpart apparent as the description progresses.

In describing'the invention in detail, reference will be'made to the accompanying drawings, in which similar parts throughout the several views are designated by similar, reference characters, generally made distinctive either by reason of distinctive exponents representative of their location or by reason of preceding numerals representative of the order of their operation, and in Which: l.

Fig. 1 illustrates in 'a diagrammatic manner the line circuits and apparatus associated therewith in a system embodying the present invention; Figs. 2A and 23, when placed end to end in theorder named, illustrate theapparatus and plurality of field stations and a control ofiiceLj Forconvenience in the description, the number of field stations has been assumed to be four,

although in actual practice a smaller or larger number could obviously be provided.

With reference to Fig. 1, a control ofiice, an intermediate field station and an end field sta- 5 tion with their interconnecting line circuits are indicated. The control oifice ,circuits are shown in detail in Figs. 2A and 2B, while the intermediate field station circuits are shown in detail in Figs. 3A and 3B. Since the last or end field station is substantially identical with an intermediate field station, with the exception of the added means included within the dotted rectangle of Fig. 3A designated End station, the details of the end field station have not been shown in a separate drawing.

Although the embodiment of the present invention illustrates the first or intermediate field station as having only a single switch and its associated signals, it should be understood that the invention is not limited to the control of only one switch and its signals at any field station but it may be extended for any desired number arranged in any suitable track layout.

For the purpose of simplifying the illustrations 2 and description, the various parts and circuits have been shown diagrammatically and certain conventional illustrations have been employed, the drawings having been made more with the purpose in mind of making it easy to understand the principles and mode of operation of such a system, than with the idea of illustratingthe particular construction and arrangement of parts that would probably be employed in actual practice. Thus, the relays and their contacts are illustrated in a conventional manner indicate the positive and negative terminals reand symbols are used to indicate connections to the terminals of batteries, or other suitable sources of electric current, instead of showing all of the Wiring connections to these terminals.

The symbols and are employed to spectively of suitable batteries or other sources of direct current. The symbol (CN) is employed to indicate a center or intermediate tap of a particular battery or source of current indicated by the (B+) and (B) symbols with which it is associated. Phose circuits connected to the terminal designated (CN) may have current flowing in one direction or the other, de-

pending upon the particular terminal (B+) or (B) of the source used in combination with this indicated intermediate tap.

Control o=17ice equipment.-The control office equipment includes a biased-to-neutral, polar line relay F which repeats the polar impulses applied to the line by battery OB. An ofiice battery selecting relay OBS of the neutral type is normally deenergized to supply current from battery 0B1 to the line circuit while the system is at rest. When relay CBS is up, the line circuit can be energized only from the field battery F3 at theend field station, assumed to be the fourth station. I

The particular polarity applied to the line circuit, either while the system is at rest or 7 supplied with potential for supplying potential to the line circuit from the ofiice battery OB. When the system is in operation, relay PC is positioned by a particular polarity during each deenergized period of the line circuit,-

7 in accordance with the message to be transmitted, so as to determine by its position the polarity of the following impulse applied to the line circuit. Relay PC is of the two position polarized type, so that its contacts remain in the positions to which they are last actuated by reason of a suitable magnetic stick type arrangement.

Irrespective of the polarity with which the line circuit is energized after the system is started through a cycle, the quick acting line repeating relays IFP and 2FP repeat each energized and each deenergized condition of the line relay F. In order that the cycles of operation may be distinctively marked ofi, slow acting line repeating relays SA and SAP are provided, which, when once energized at the beginning of a cycle, remain energized throughout the cycle, irrespective of the brief deenergizations of the line circuit between the several impulses.

A suitable step-by-step means is employed being specifically embodied in a stepping relay bank including relays IV, 2V, 3V, 4V and 5V together with a half step relay VP. The half step relay is caused to shift its position upon each energization of the line circuit, while the stepping relay bank is caused to take one step following each energization, that is, during the deenergized period between the successive impulses applied to the line circuit.

The control impulses are suitably time spaced and measured by impulsing relay E, impulse repeating relay EP and the actual response of the stepping relay bank in the control ofiice. The maximum length indication impulses (long) are time spaced and measured by the impulsing relay E, the repeating relay EP, an impulse prolonging relay EPT and the actual response of the stepping relay bank in the control office. The minimum length indication impulses (short) are time spaced and measured by the impulsing relay E and the actual response of the stepping bank at the field station which is transmitting the indications.

The control ofiice also includes a lock-out relay L0 and a slow acting repeating lock-out relay LOP for purposes hereinafter pointed out in connection with the lock-out features of the system.

The transmitting and receiving equipment located in the control ofiice is made available for effective use by the operator, by providing a suitable control machine having mounted thereon a miniature track diagram of the actual track layout in the field, together with the control levers, buttons and the like which are manually operable to obtain the desired transmission of controls. As typical of such a control machine, a miniature track switch is, a switch machine control lever SML, and a signal control lever SGL have been shown, these devices being associated with the corresponding trafiic controlling devices at the assumed first intermediate field station illustrated in Figs. 3A and 3B.

The control machine preferably has a starting button SB associated with each group of control levers associated with a particular field station, so that, when the control levers for that station are properly positioned in accordance with the positions to which it is desired that the corresponding traffic controlling devices shall be operated, the starting button SB may be depressed thereby causing the transmission of suitable controls to the corresponding field station.

Instead of showing the actual circuits and means associated with the several starting buttons of such a system for accomplishing the initiation of the system and allowing the transmission of controls to only one station at a time, such control has been merely indicated. The means usually provided to obtain these results includes a storing relay such as relay SR and a code determining relay such as relay CD one of each for each starting button such as SB. The relays SR and CD for a station group of control levers are so interlocked with the corresponding relays SR and CD for other stations, that only one code determining relay can be energized at any one time, irrespective of the number of storing relays which are energized. This is because the starting buttons may be actuated at any time, which fact is stored by the corresponding storing relay, but only one of the storing relays can be eifective to energize its corresponding code determining relay, so that only one station code call is transmitted at a time.

Such an arrangement of code determining relays, actuated one at a time either by a starting button such as starting button SB, or by the movement of an associated control lever, has been completely shown in prior applications, such for example as in the pending application of N. D. Preston et al., Ser. No. 455,304, filed May 24, 1930, corresponding to Australian Patent 1,501 of 1931. It is believed, however, that the above discussion of these SR and CD relay functions is sufiicient for an understanding of the operation of the present invention.

Also, located on the control machine are suitable indicator lamps, such as lamps N and R for indicating the normal and reverse positions of the track switch TS in the field, when illuminated, and for indicating the unlocked condition of that track switch when both lamps are unilluminated. An indicator lamp OS indicates, when illuminated, the occupied condition of the associated detector track section in the field.

These indicator lamps, as well as other type indicators, are controlled by suitable indication storing relays, such as relays IIR, 21R. and 31R,

-' which are of the two position polarized type. A

group of these indication storing relays are associated with each control panel allotted to a field station and are rendered efiective to receive the indications transmitted whenever the corresponding station is allowed to transmit its indications.

Whenever a field station is conditioned to transmit, it first transmits its code call which is registered in the control office by suitable pilot relays, such as pilot relays IPT and 2PT. At the end of the transmission of the station code, the pilot relays are in position to select the proper station storing relay, such as relay ST assumed, associated with the station illustrated in Figs. 3A and 3B.

The control ofiice includes a plurality of control code sending buses IOI, I02, I03, I04, and I05 which are energized in accordance with the position of the code jumpers and control levers for controlling the selection of a station and the transmission of controls thereto.

Indication code receiving buses I3I, I32, I33, I3 3, and I35 are energized in accordance with those indications which are transmitted from a field station by impulses distinctive for their polarity, while indication buses I2I, I22, I23, I24, and I25 are energized in accordance with those indications which are transmitted from a field station by impulses distinctive for their duration.

Other devices and apparatus include suitable code jumpers, buses, overload protection and such other means as may be considered adjuncts to a system of this type, but which need not be considered in their specific form for an understanding of the present invention.

Intermediate fie'ld station equipment.-With reference to Figs. 3A and 3B of the accompanying drawings an intermediate field station, more specifically considered as the first field station, has been shown as typical of all intermediate field stations. This first field station includes a track switch TS which is operated by a switch machine SM of any suitable type, such for example as disclosed in the patent to W. K. Howe, Patent No. 1,466,903 dated September 4, 1923. The switch machine may, if desired, be provided with a dual control selector, as disclosed for example in the pending application of W. K. Howe, Patent No. 1,852,573, filed April 10, 1929 so as to permit the manual operation of the track switch.

The position of the track switch is repeated by the usual switch repeating relay WP of the polar neutral type. This relay is preferably controlled by a polarized circuit including suitable point detector contacts or switch box contacts (not shown) so that the relay is energized with I one polarity or the other depending upon the normal or reverse extreme positions of the track switch, and so that it is deenergized whenever the track switch is unlocked or is in operation.

The track switch has associated therewith the usual detector track section having a track battery and a track relay T included in a normally energized track circuit.

The traffic over the track switch is governed is in a clear or proceed position, this relay is deenergized. Similarly, the signals 2A and 23 have associated therewith a signal repeating relay 2M which is energized with both of these signals at-stop, but which is deenergized whenever either of these signals is in a clear or proceed position. Although these signals IA ---IB and 2A 2B have been illustrated as being of the semaphore type, it is to be understood that they may be of the light signal type or any other suitable type for governing traific in accordance with the usual practices.

Although approach track sections have not been illustrated in the drawings as associated with the track switch TS such approach track sections are preferably employed, having associated therewith suitable annunciator track relays such as relays IAT 2AT and 2BT The relay I AT may be considered as associated with an approach track section in advance of the signals I A IB the relay 2AT may be considered as associated with an approach track section in advance of the signal 2A and the relay 2BT may be considered as associated with an approach track section in advance of the signal 2B The communication part of the systemincludes,

of the polarity with which it is energized, while a slow acting line repeating relay SA is energized at the beginning of each cycle of operation and is maintained picked up until the end of that cycle.

The field station is provided with a bank of neutral stepping relays 1V 2V 3V QV and SW, together with a half step relay VP This bank of neutral stepping relays takes one step for each deenergized period of the line circuit during a cycle, each step being taken in synchronism with the corresponding step at the control ofiice. However, the stepping operation at each station is discontinued as soon as that field station fails to be selected for reasons hereinafter pointed out. The half step relay shifts its position upon each energized period of the line as long as the step-by step operation at that station continues.

For the purposes of lock-out, so as to permit only a single station or the control ofiice to transmit during any one cycle, a lock-out relay L0 and a selecting relay S are provided, these relays being responsive to the particular conditions of initiation imposed upon the line circuit at the beginning of each cycle. A lock-out repeating relay LOP is associated with the lockout relay L0 for reasons hereinafter to be explained.

A relay P is provided for pulsing the line circuit in accordance with certain of the indications to be transmitted, While a pole changing relay P0 is provided for determining the polarity of the impulses in accordance with certain other of the indications to be transmitted.

For the purpose of storing any change in conditions which may occur in the traffic controlling devices to be indicated, a change relay CH and a change repeating relay CI-lP are provided. In the event that a particular traffic controlling device is of such a character that the condition to be indicated is transient or temporary, a suitable storing relay may be provided, such as illustrated by the relay TR associated with the track relay T Each station equipment is provided with station code receiving relays, which are responsive to the station code calls transmitted over the line circuit for completing selecting circuits so long as the particular code call transmitted corresponds to the code call assigned to that station. Any station may be made responsive to any particular code call of which the system is capable of transmitting by the proper positioning of its station selecting code jumpers. These station code receiving relays for the first intermediate field station, include relays EST and 2ST which are of the two position polar magnetic stick type.

The controls transmitted for the trafiic controlling devices in accordance with the position of the levers in the control ofiice are received by suitable two-position polarized relays preferably of the magnetic stick type, which in turn govern their associated devices. For example, the relay SMR is responsive to the position of the control lever SML and this relay governs the actuation of the switch machine SM to normal or reverse positions. Similarly, the signal relay SG and the direction relay DB are responsive to the position of the signal lever SGL and serve to govern the signals [A -4B and 2A 2B which control has been merely indicated by a dotted line. This indicated control of the signals is understood to include suitable approach locking, suitable automatic block signalling control and such other adjuncts to a centralized trafiic control system, as may be required to accomplish the usual protection for the movement of trains, all of which has been more specifically set forth in the pending application of S. N. Wight, Ser. No. 120,423, filed July 3, 1926.

Each intermediate field station includes a resistor such as R which is of a value dependent upon the distance of that field station from the field battery FB. The line circuit includes, during a certain period at the beginning of each indication cycle of operation, only the line wire up to the station nearest the end of the system which has indications ready to transmit, and a resistor such as R at such station must be provided to limit the current fiow in the line thus decreased in length, in order that the proper current value may be maintained in the line relays. The particular value of these resistors is determined in accordance with the usual engineering practices.

Each field station includes a group of control code receiving buses, such as buses 20!, 202, 293, 2%, and 2&5 which are energized in accordance with the controls received from the control ofiice.

Also, indication code sending buses 23l, 232, 233, 234, and 235 are energized in accordance with those indications which are transmitted from the field station by impulses distinctive for their polarity, while the indication code sending buses 225, 222, 223, 224, and 225 are energized in accordance with those indications which are transmitted from the field station by impulses distinctive for their duration.

End field station equipment.As previously mentioned, the end field station is the same as an intermediate field station insofar as the communication part of the system is concerned, with the addition of the apparatus included within the dotted rectangle of Fig. 3A given the legend End station, together with the circuit connections coordinating it with the rest of the station.

This added apparatus includes a field battery F5 and a field battery selecting relay FBS This field battery selecting relay serves to connect the battery FB into the line circuit during an indication cycle. The control of relay FBS is accomplished by the same apparatus provided at other stations through the medium of suitable connecting circuits.

In the event that the last field station for receiving controls and transmitting indications is unsuitable for the location of the field battery F13 it is consistent with the present invention to provide an end field station only for the control of the field battery. In other Words, only those devices of Fig. 3A which furnish control for the relay FBS are required at such an end station. It is believed unnecessary to illustrate such a station as the means required for the control of relay FBS will be evident from the following description.

It is believed that further description will make the invention best understood by setting forth various typical operations of the system.

Operation of the system The system of the present invention is normally in a condition of rest, but may be initiated into a cycle of operations either from the control ofiice or from any of the field stations Whenever.

there are new controls or new indications respectively to be transmitted.

Although new controls and indications may occur simultaneously, the system is so arranged that only controls or indications may be trans mitted during any one particular cycle. In case new controls and indications become ready for transmission simultaneously, the system is so arranged that the resulting cycle is for the transmission of indications, while the succeeding cycle or cycles, as the case may be, will be for the transmission of the new controls. In other words, indication conditions are superior to control conditions only when such conditions occur simultaneously, but if there are a plurality of stations to receive controls, the operator may cause such controls to be transmitted irrespective of the presence of any new indications which may occur at any one or several of the field stations during such transmission.

While the system is normally at rest, the line circuit is energized with negative potential. Such energization, after a continued deenergizae tion of the line circuit at the end of a cycle of operation, is effective to set the system in readiness for the initiation of a cycle either from the control oifice or from some field station.

For convenience in describing the present invention, a positive impulse applied to the line circuit in the control ofi'ice (see Fig. 1) will be considered as current flowing from left to right in the line wire l2, which positions the line relays F (with suitable exponents) to the right, while a negative impulse will be considered as current flowing from right to left in the line wire l2 and the line relays F (with suitable exponents) will be positioned to the left.

When the system is initiated into a cycle of operations, distinctive initiating conditions are set up, depending upon whether the cycle is to be for the transmission of controls or the transmission of indications. If the cycle is to be for the transmission of controls, the current in the line circuit is quickly reversed, that is, the normal negative energization of the line circuit is changed to a positive energization. This positive energization of the line circuit is continued for a predetermined period of time suflicient for all of the field stations and the control oifice to be in readiness to enter a control cycle, at which time the line circuit is deenergized. For convenience in describing the present invention, the period of time which is required for the reversal of the energization of the'line circuit, plus the period of time during which the positive energization of the line circuit is continued, will be considered as the initiating period. In other words, the initiating period extends from the period of rest up to the first continued deenergization of the line circuit.

60 On the other hand, if an indication cycle is to be initiated, the line circuit conditions throughout the system vary as more specifically pointed out hereinafter, but in general it may be stated that the time before the reversal of the line D circuit current, that is, before a positive energization thereof, is of somewhat longer duration, after which the line circuit is energized with positive energy. Similarly in this case, that period of time required for the reversal of the current in the line circuit, up to the first continued deenergization after the application of the first posi-' is conveniently termed the the character of the cycle to follow includes a positive energization of the line circuit and the end of such energization is the end of the initiat-x ing period. The first deenergization of the line circuit following the initiating period, causes the step-by-step mechanisms at the control o ifice and at the field stations. to take the first step in,

For convenience in describing the present invention, each deenergization of the line circuit will be referred to as an off period and each energization of the line circuit will be referred to as an on period. In this Way the variousrelay operations of the system may be designatedas occurring either during the initiating on and off periods or during a particular off or on period of each step, in each case the reference being made to the condition of the line circuit.

The description of the operation of the system is also facilitated by considering that each step is divided into a conditioning period and an executing period. The conditioning period is the first part of the step, that is, the off period during which the: various relays are being conditioned in readiness for the transmission of :theynext message. The stepping relay corresponding to the particular step is picked up during the; off period. The executing period of each step is the second part of that step, that is, the on period, during which the character of the impulse applied to the line circuit is efiective to position the message storing relay which is to-be controlled on that particular step. The W? relay associated with: the stepping relay bank in the control ,officeis' shifted during each on period, beingpicked up during the initiating and even on periods, and dropped during odd on periods. relay at the station is shifted'during each onj period (after the initiating period) It is picked up during each odd on period and dropped dur-. ing each even on period. I

Normal cat-rest condition-With the system in;

its normal or period of blank condition, the line I stations to their left hand full line-positions. Re-' ferring to Fig. 1, this circuit extends from the terminal of battery OB, contact 2! of'relay PC in its left hand position, back contact 2 of relay OBS, line conductor Ml, back contact 2? of relay PC at the intermediate field station,- conductor 20, back contact 3! of relay PC at the end field station, back contacts 32 and 34 of relay FBS back contact 38 of relay'PC winding of; relay F back contact 40 of relay P conductor 22, back contact 4! of relay PC winding of relay F back contact of relay P conductor l 2, normally closed front contact ll of relay "EP; winding of relay F, back contact of relay CBS and contact 53 of relay PC in its left hand'position, to the terminal of battery OB. "This circuit may also be traced on Figs. 2B and 3A, with the exception of certain contacts and relay windings not included, due to the fact that the complete line circuit through the intermediate and end field stations is not shown in these two' figures. H Relay PC (Fig. 2B) is energized with currentflowing in the proper direction for positioning The VP which extends from (CN) winding of relay PC, conductor 90, back contacts 89, 88, 81, 85, and of relays 5V, 4V, 3V, 2V, and IV respectively, conductor 84, back contact 83 of relay SR back contact 8| of relay SR conductor 80, front contact I9 of relay LOP and front contact I? of relay L0, to' (B-).

Relay EP is energized by means of a circuit extending from back contacts 23 and 25 in multiple of relays OBS and IF? respectively, upper winding of relay EP and front contact 25 of relay E, to Relay L0 is normally energized by means of a. circuit extending from contact 55 of relay F in its left hand position, back contact 51 of relay SA and upper winding of relay L0, to Relay LOP is normally energized by means of a circuit extending from back contact 66 of relay SAP, front contact 59 of relay L0 and winding of relay LOP, to Relay E is normally energized by means of a circuit extending from back contacts 9|, 92, 93, 94, and of stepping relays 5V, 4V, 3V, 2V, and IV respectively, lower Winding of relay E and back contact 99 of relay VP, to

At the field station, relay LO is normally energized by means of a circuit extending from contact I'lfl of relay F in its left hand position, back contact I72 of relay SA and lower winding of relay L0 to Relay LOP is normally energized by means of a circuit extending from contact I'Iil of relay F in its left hand position, back contact I'l2 of relay SA, front contacts I19 and I'M of relay L0 and winding of relay LOP to Relay CH is normally energized by means of a circuit extending from contacts I50, I5I, I52, I53, I54, I55, and I55 of relays 2BT ZAT lAB 2M IM WP, and TR respectively in either their front or back point positions, front contact I58 and upper winding of relay CH to These six relays are assumed to be normally energized by means of circuits which are not shown, since they are familiar to those skilled in the art and since the detailed circuit arrangements for operating these relays are immaterial for the understanding of the present invention.

It will be assumed that the operator in the control ofiice desires to move the track switch TS at the station indicated in Fig. 3B from a normally locked position to a reverse locked position. The normally locked position of the track switch is typified by the contacts of relay WP being in the full line positions shown. After a discussion of the circuit operations effective to select the station and thereafter actuate the switch machine, resulting in a change in the position of the polar contacts of relay WP an explanation of the operation of the system relating to the transmission of indications back to the control office due to such a change in condition will be given.

Manual start.With the system in its normal condition, the actuation of starting button SB is effective to pick up the corresponding storing relay SR followed by the picking up of the corresponding code determining relay CD This initiates the system into a cycle of operations and determines the code which is to be transmitted over the line circuit for the selection of the particular field'station associated with button SB and levers SML and SGL. It will be understood that the storing relays can be picked up at any time the corresponding starting buttons are actuated, but only one code determining relay may its contacts to the left as shown, over a circuit be energized at one time and only while the system is in its normal condition. The particular code determining relay which will be picked up at the start of an operating cycle, when several stations are to be selected, is determined by the interconnection of these code determining relays as disclosed in the prior application of N. D. Preston et al., Ser. No. 455,304, filed May 24, 1930.

The picking up of relay SR momentarily opens the above described energizing circuit for relay PC and immediately establishes another energizing circuit for this relay of reversed polarity. The energizing circuit for relay PC now extends from (B+), front contact 8I of relay SR back contact 83 of relay SR and over the remainder of the above described circuit to the winding of relay PC, Relay PC quickly shifts its contacts H and 53 to their right hand dotted positions, which is effective to momentarily deenergize the line and thereafter again energizing it with potential applied to conductor I2 and potential applied to conductor IE1. This circuit extends from the terminal of battery OB, contact 2! of relay PC in its right hand dotted position, back contact 58 of relay OBS, winding of relay F, front contact 41 of relay EP, line conductor I2 and through the above described circuits at the field stations, line conductor II], back contact 24 of relay OBS and contact 53 of relay PC in its right hand dotted position to the terminal of battery OB.

This reversal of current in the line circuit marks the end of the normal period and the beginning of the initiating period. The line relays in the control oiilce and at the field station are now actuated to their right hand dotted positions. A circuit closed for picking up relay I FP which extends from contact 55 of relay F in its right hand dotted position and winding of relay IFP, to A circuit is closed for picking up relay ZFP which extends from front contact IT of relay IFP and winding of relay ZFP, to Relay SA is picked up by means of a circuit extending from front contact 43 of relay ZFP and winding of relay SA, to Relay SAP is picked up by means of a circuit extending from front contact I8 of relay SA and winding of relay SAP, to

The actuation of contact 55 of relay F from its left hand position opens the normal energizing circuit through the upper winding of relay LO, but this relay is not released due to the fact that relay F closes a stick circuit for relay LO extending from contact G'I of relay F in its right hand dotted position, back contact 28 of relay SA, front contact 42 and upper winding of relay L0, to As soon as relay SA is picked up, another stick circuit is closed for relay LO which is effective throughout the cycle and which extends from front contact I8 of relay SA, front contact 39 and lower winding of relay L0, to Relay L0 is slightly slow releasing due to the short circuit around its lower winding which extends from back contact I8 of relay SA, front contact 39 of relay L0 and lower winding of relay L0, to To obviate any chance of relay LO dropping its armature when this short circuit is removed at the time relay SA picks up and opens its back contact I8, the arrangement and adjustment of back contact 28 may be such that it is not opened until after front contact I8 is closed.

During the initiating period, a circuit is closed for picking up: relay VP which is effective as soon as relay SAP has been picked up and which extends from (3+), front contact 29 of relay SAP, back contacts 1|, 12, 13, 14 and 15 of the five stepping relays in series, upper winding of relay VP and front contact 44 of relay ZFP, to (CN). Relay VP closes a stick circuit for itself extending from front contact 66 of relay SAP, front contact 48 and lower winding of relay VP, to It will be noted that the current flow through both windings of relay VP at this time is in the same direction.

The actuation of the VP relay contacts opens the above described energizing circuit of relay E at back contact 99, allowing relay E to drop, which in turn causes the dropping of relay EP by opening the above described energizing circuit of this relay at front contact 26 of relay E. This marks the end of the initiating period and the beginning of the first off period, by deenergizing the line circuit at front contacts 31 and 41 of relays E and EP respectively.

Relay LOP is deenergized and drops its contacts when relay SAP is picked up, due to this latter relay opening the above described energizing circuit of relay LOP at back contact 66 of relay SAP. Relay LOP remains down until the change to normal period at the end of the cycle when it is again picked up as will be later described. Relays EPT and OBS remain down throughout this cycle.

While all this has been taking place at the control office, the field station circuits have likewise been functioning to prepare for the cycle of operations which follows. Although the de' scription will be specifically directed to the field station illustrated in Figs. 3A and 3B, it Will be understood that similar operations take place at the other stations along the line (with exceptions later pointed out).

When relay F is actuated to its right hand 40 dotted position in synchronism with relay Fin the control ofiice, a circuit is closed for picking up relay FP which extends from contact I'll of relay F in its right hand dotted position and Winding of relay FP to Relay FP closes a circuit for picking up relay SA which extends from front contact I16 of relay FP and Winding of relay SA to When relay F actuates its contact I1E, away from the left hand position, it interrupts the above described energizing circuit through the lower winding of relay L0 but establishes a stick circuit for this latter relay before it has time to release which extends from contact I1I of relay F in its right hand dotted position, back contact I13 of relay SA front contact I19 and lower windback contact I85 of relay 3V conductor 181,

front contact I88 of relay SA front contact I99 and upper winding of relay L0 to It is obvious that the contacts of relay SA may be so arranged and adjusted that this circuit is established at front contact I82 before the above described stick circuit through back contact I13 of relay SA is broken. Relay LOP is deenergized and drops its contacts after a predetermined time interval, due to the interruption of the above described energizing circuit for this relay at back contact I13 of relay SA Relay VP is not picked up during the initiating period. Its pick-up circuit is first established during the first on period as will later be described.

Impulsing and stepping operations.1t will be recalled that the system is advanced into the first off period when relay EP drops to deener gize the line. This causes relay F to restore its contacts to their deenergized positions, which opens the energizing circuit of relay I FP at contact 55 of relay F. Relay IFPdrops and causes the release of relay ZFP by opening the energizing circuit of this latter relay at contact I1 of relay IFP. The release of relay ZFP opens the energizing circuit of relay SA at front contact 43, but relay SA (because of its slow releasing characteristics) is not dropped before relay ZFP is again picked up to reestablish this energizing circuit. This same condition is effected during all of the impulse periods, so that it is unnecessary to repeat the explanation in connection with each impulse during the cycle.

The release of relay ZFP closes a circuit for picking up stepping relay IV which extends from back contact 43 of relay ZFP, front contact I5 of relay SA, back contact 38 of relay EP, front contact 49 of relay VP, back contact 52 of relay 4V, back contact 54 of relay 2V and winding of relay IV, to Relay IV establishes a stick circuit for itself extending from front contact 66 of relay SAP, front contacts 59 and winding of relay IV, to

Relay IVinterrupts the above described energiz ing circuit of relay PC at its backcontact but immediately reestablishes another energizing circuit for relay PC at front contact 85, which circuit is dependent for the selective positioning of relay PC upon the code jumper connections as will be later explained. It will be assumed, however, that relay PC is actuated to one position or the other during each off period for connecting battery OB to the line circuit when impulsing relay E closes its front contact 31 for energizing the line circuit.

Relay IV establishes an energizing circuit for relay E which extends from back contacts SI, 92, 93, and 94 of relays 5V, 4V, 3V, and 2V respectively, front contact 95 of relay IV, upper winding of relay E and front contact 99 of relay VP, to Relay E picks up and closes a circuit for picking up relay EP extending from back contact 23 of relay OBS, upper winding-of relay EP and front contact 26 of relay E, to

The picking up of relay E closes the line circuit at its front contact 31, which extends through make-before-break back contact 41 of relay EP and over the remainder of the previously described circuit through contacts 2! and 53 of relay PC to battery OB. Relay EP in picking up maintains the continuity of the line circuit by closing front contact 41 before opening back contact 41;

'This marks the end of the first off period and the beginning of the first on period by energizing the line circuit. Relay F- actuates' its contacts to either their right or left hand positions (as will be later explained), so that a circuit is closed for picking up relay IFP which extends from contact 55 of relay F and winding of relay IFP if contact 55 is positioned to the right, but if contact 55 is positioned to the left, the circuit extends through front contact 51 of relay SA to the winding of relay IFP.

Relay HFP again closes the above described energizing circuit for relay 2FP.

The picking up of relay ZFP closes a circuit 5 which is effective to release relay VP, which circuit extends from (CN), front contact 44 of relay 2FP, upper winding of relay VP, back contacts l5, l4, l3, and 12 of relays 5V, 4V, 3V, and 2V respectively, front contact ll of relay IV and 10 front contact 46 of relay VP, to (B). Recalling that the lower winding of relay VP is energized by potential applied to the right hand terminal of this winding and noting that potential is now applied to the right hand terl5 minal of the upper winding, it will be apparent that these two windings oppose with the result that the relay is restored to its deenergized position.

The dropping of relay VP opens the above described energizing circuit of relay E at front contact 99, so that relay E is dropped and by opening front contact 25, the energizing circuit of relay EP is interrupted and this latter relay is released.

This marks the end of the first on period and the beginning of the second off period by opening line conductor I2 at front contacts 3'! and 41 of relays E and EP respectively. Relays F, IFP, and ZFP are now deenergized as above 30 described. Relay 2V is now picked up by means of a circuit extending from back contact 43 of relay EZFP, front contact l of relay SA,

back contact 38 of relay EP, back contact 49 of relay VP, back contact 5| of relay 5V, back contact 56 of relay 3V, front contact 58 of relay IV and winding of relay 2V, to Relay 2V establishes a stick circuit for itself, by way of its front contact El, to at front contact 66 of relay SAP. Relay E is again picked up by means of a circuit extending from back contacts 9|, 9?. and 93 of relays 5V, 4V and 3V respectively, front contact 94 of relay 2V, lower winding of relay E and back contact 99 of relay VP, to The picking up of relay E again 45 closes the above described circuit for picking up relay EP and the above described circuit for en ergizing the line is again established, to mark the end of the second off period and the beginning of the second on period. so Relays F, WP, and ZFP are again picked up by means of the previously described circuits. Relay VP is picked up over a circuit extending from (CN), front contact 44 of relay ZFP, upper winding of relay VP, back contacts 15, I4, and 13 of relays 5V, 4V, and 3V respectively and front contact 12 of relay 2V, to (B+). Relay VP establishes the above described stick circuit for itself by closing its front contact 48. The energizing circuit of the lower winding of relay co E is now interrupted at back contact 99 of relay VP, so that relay E is dropped and the above described energizing circuit for relay EP is again interrupted to cause the release of this relay.

This marks the end of the second on pen; riod and the beginning of the third off period. Relays F, IFP, and 2FP again release and a circuit is closed for picking up relay 3V which extends from back contact 43 of relay ZFP, front contact l5 of relay SA, back contact 38 of relay EP, front contact 49 of relay VP, back contact 52 of relay 4V, front contact 54 of relay 2V and winding of relay 3V, to Relay 3V establishes an obvious stick circuit for itself at its front contact 62. The energizing circuit 75 through the upper winding of relay E is now established which extends from back contacts 9| and 92 of relays 5V and 4V respectively, front contact 93 of relay 3V, upper winding of relay E and front contact 99 of relay VP, to

The actuation of relay E again closes the circuit I for picking up relay EP.

The line is again energized to mark the end of the third off period and the beginning of the third on period. Relays F, IFP, and ZFP are again picked up and relay VP is dropped by establishing a, circuit through its upper winding, which is in opposition to that in its lower winding and which extends from (CN) front contact 44 of relay ZFP, upper winding of relay VP, back contact 15 of relay 5V, back contact 14 of relay 4V, front contact 13 of relay 3V and front contact 46 of relay VP, to (B-). The energizing circuit through the upper winding of relay E is now interrupted at front contact 99 of relay VP so that relay E drops and in turn causes the dropping of relay EP.

This marks the end of the third on period and the beginning of the fourth off period. Relays F, IFP, and ZFP are now released and a circuit is closed for picking up relay 4V which extends from at back contact 43 of relay ZFP, over the remainder of the previously described circuit to contact 56 of relay 3V and since relay 3V is picked up, this circuit is extended through front contact 5'3 of relay 3V and the winding of relay 4V, to Relay 4V establishes an obvious stick circuit for itself by Way of its front contact 63. Relay E is now picked up by means of a circuit which extends from back contact 9| of relay 5V, front i tact 44 of relay ZFP, upper winding of relay VP,

back contact 15 of relay 5V and front contact 74 of relay 4V, to (B+). Relay VP again establishes the above described stick circuit for itself and also opens the energizing circuit through the lower winding of relay E at back contact 99.

Relays E and EP are now released to deenergize the line.

This marks the end of the fourth on period and the beginning of the fifth off period. Relays F, IFP, and 2FP are again dropped in turn, after which a circuit is established for picking up relay 5V, which circuit has been previously described up to contact 52 of relay 4V and which now extends through front contact 52 of relay 4V and the winding of relay 5V, to Relay 5V establishes an obvious stick circuit for itself by way of its front contact 64. An energizing circuit is now established for relay E from front contact 91 of relay 5V, upper winding of relay E and front contact 99 of relay VP, to which circuit is effective to pick up relay E, after which relay EP is picked up. The line is now energized as previously described.

This marks the end of the fifth off period and the beginning of the fifth on period. Relays F, IFP and 2FP again pick up and the previously described circuit for effecting the release of relay VP is established, with the potential applied to the right hand terminal of the upper winding of relay VP now completed through front contact 15 of relay 5V. Relays- E and EP are now released in turn, since the dropping of relay VP interrupts the above described ener gizing circuit through the upper winding of relay E at front contact 99 and the line deenergized.

This marks the end of the fifth on period and the beginning of the change to norma 01? period. Relays F, IFP, and 'ZFP again release but this time there is no stepping relay to be picked up. maining down because there is no circuit for energizing relay E through its lower winding with relay VP down and relay 5V up. Since relays E and EP can not be picked up, the line is not again energized, so that relay ZFP remains down for a sufficiently long time interval to cause the release of relay SA by opening its energizing circuit at front contact 43 of relay ZFP. Relay SA interrupts the energizing circuit of relay SAP at its front contact I8, with the result that relay SAP is dropped after a predetermined interval of time.

The dropping of relay SA opens the stick circuit of relay LO at front contact l8 and after a short time interval, relay L0 is dropped. All the stepping relays are dropped when relay SAP releases and opens their stick circuits at front contact 66. A circuit is now completed for picking up relay E extending from through back contacts 9|, 92, 93, 94 and 95 of the five step-' ping relays in series, lower winding of relay E ning of the normal on period. If there are no;

other storing relays picked up, relay PC will actuate its contacts to their left hand positions by means of the previously described circuit which exists during the normal condition of the system. This effects the energization of the line.

circuit with a potential applied to conductor 12 from battery OB, for positioning the line relay contacts to their left'hand positions.

Since relay SA is down and relay F is in its left hand position, there is no circuit for energizing relay EFP. Relay IFP and relay ZFP remain down until the start of another cycle. Relay LO now has its original energizing circuit established by way of contact 55 of relay Fin its left hand position. Relay LOP has its original energizing circuit established by way of back contact 8% of relay SAP and front contact 69 of relay LO. Relays L0 and LOP are picked up.

It is not believed necessary to describe in de tail the stepping relay operations at the field station, since these relays are picked up by means of circuits similar to the circuits of corresponding relays in the control office. It will be understood that relays F and FP operate substantially in synchronism with relays F and ZFP in the control office so that circuits similar to those above described are completed for picking up and sticking the five stepping relays of Fig. 3B.

The pick-up circuits for the .odd stepping relays at the field station extend through back contact 2 t of the half step relay VP instead of through a front contact as is the case in the control office. lays at the field station are picked up through This results in relays E and EP re-n Likewise, the even stepping rea front contact (260) of the VP relay instead of a back' contact (49) as in the case of the control oflice stepping relay operation. This is due to the fact that the half step relay at the field station is picked up first during the first on periodafterthe first stepping relay has been picked up, so that it is necessary to extend the circuits to the odd stepping relays through a contact of the half step relay that is closed when this relay is down. The pick-up and opposing circuits for relay VP are similar to those described for-relay VP. The pick-up circuits for the stepping relays at the field station are completed through either front contact 251 of relay LO. or front contact 256 of relay S This results in the stepping relay operation being stopped at those stations which are not to be selected during a control cycle, as determined by both relays L0 and S being down as'will be later explained.

'jStOIGd ofiice start conditions-4n the event that there are one or more storing relays up when the system advances into its change to normal" period, it does not go into its normal condition but passes directly from the change to normal period of one cycle into the initiating period of the next cycle. This results in the line relays being positioned to the right as above explained in connection with the initiating period.

Itwill be assumed that relay SR is up when the above described cycle reaches its change to normal period, due to a stored office start condition awaiting transmission. ping relays drop, the previously described circuit through their back contacts 89, 88, 81, 86, and to the winding of relay PC is not completed to (3-) byway of conductor 80, due to back contact 83 of relay SR being open. "The circuit of relay PC is completed to (3+) at front contact 33 of relay SR so that relay PC is positioned to the right for energizing the line with potential which actuates line relay F to the right.

Relays'lFP, ZFP, SA, and SAP now pick up. Relay LO does not pick up because its pick-up circuit through contact 55 of relay F in its left hand position is not closed before the circuit is opened at back'contact 51 of relay SA. Relay LOP remains down because its pick-up and stick circuits are open at back contact 66 of relay cycle is reached, with no storing relay up, then (B) through back contact 19 of relay LOP and back contacts of all storing relays in series is applied-to the winding of relay PC over the previously"described circuit. This positions relay PC 'to'the left and restores the system to its normal condition by energizing line l2 with potential which is effective to position the line relays to the left. The previously described circuits are now effective to pick up relays L0 and LOP.

The circuit which normally energizes the lockout relays at the stations (such as relay L0 of Fig. 3A) has been previously described. As will be later explained, only the lock-out relay associated with the station selected during a particular cycle remains up throughout that cycle.

This particular lock-out relayis dropped during the change to normal period because the energizing circuit of its upper winding is open at front contacts I82 and I88 of relay SA and the 5 energizing circuit of its lower winding is open at contacts I18 and I II of relay F now deenergized.

If the system is restored to its normal condition at the end of a cycle, all lock-out relays are I0 picked up during the normal period over circuits similar to that shown in Fig. 3A which extends from contact I'IO of relay F in its left hand position, back contact I12 of relay SA and lower winding of relay L0 to d 15 If the system starts another cycle without returning to normal, the line relays are not positioned to the left before the SA relays are picked up. The lock-out relays are picked up during the initiating period over circuits similar to that of Fig. 3A which extends from back contact I82 of relay SA front contact I 8| of relay FP back contact I80 of relay LOP back contact I12 of relay SA and lower winding of relay LO to Stick circuits of the look-out relays are established similar to that extending from front contact I82 of relay SA conductor I83, back contact I85 of relay 3V conductor I81, front contact I88 of relay SA front contact I90 and upper winding of relay L0 to Front contacts I82 and I88 of relay SA are so organized that they make before back contacts H82 and H2 break.

Briefly, relay L0 in the control oflice is up when the system is in its normal condition and remains up during a cycle, irrespective of the station selected. It is dropped and again picked up during the change to normal period if there are no office start conditions waiting. It is not again picked up in the change to normal 40 period but remains down during the next cycle if there is an ofiice start condition waiting. Relay LOP is up when the system is in its normal condition, is deenergized during the initiating period, remains down during the cycle until the change to normal period, when it is picked up if there is no ofiice start condition waiting, but remains down during the next cycle if there is an office start condition waiting.

At the field station, the lock-out relays and the lock-out repeating relays are up when the system is in its normal at-rest condition. The lock-outrepeating relays at all stations are dropped during the initiating period of a cycle, remain down throughout the cycle until the change to normal period, when they are picked up if there is no ofiice start condition waiting. They are not picked up until a change to normal period is reached with no ofiice start condition waiting.

The lock-out relays at those stations not selected during a cycle are dropped out during that cycle as will be later explained, only that lockout relay associated with the selected station remaining up until the change to normal period,

when it is dropped. The lock-out relays at all stations are again picked up during the change to normal period if there are no office startconditions awaiting transmission, or if there is an office start condition waiting, these lock-out relays are all picked up during the initiating period of the following cycle.

This operation of the lock-out and lock-out repeating relays will be later referred to in connection with the transmission of indications, be-

cause the reason for this particular operation is to prevent a fieldstation obtaining access to the communication circuit when it is being used to transmit controls and as long as there are stored controls waiting to be transmitted.

Transmission of controls.Itwill be recalled that the lock-out relays such as relay LC of Fig. 3A at all field stations are up during the initiating period of each cycle. sumed that the station shown in Figs. 3A and 3B is to be selected and the switch machine at this station moved from its normal locked position to its reverse locked position. The illustrated station is assumed selectable in response to a and a impulse applied to line I2 during the first two steps of the control cycle, as determined by code jumpers 35 and 33 of Fig. 2A being connected to (B) and (B+) respectively as shown. The connection of code jumper 2II] of Fig. 3B from contact 2II of relay 2ST in its right hand position to bus I81 determines that this particular station responds to the code combination It will be further assumed that the stepping relays in the control ofiice and at the illustrated field station operate in synchronism throughout the cycle as above explained. The impulse to be applied to the line circuit during the first on period is determined during the preceding off period by relay PC of Fig. 23 being actuated to the left over a circuit extending from (CN), winding of relay PC, conductor 90, back contacts 89, 88,- 81, and 86 of relays 5V, 4V, 3V, and 2V respectively, front contact of relay IV, conductor IOI, front contact 3I of relay CD and code jumper 35 in its full line position, to (B-). When line I2 is energized during the first on period, relays F and F will be positioned to the left because the terminal of battery OB is connected by way of contact 53 of relay PC in its left hand position, back contact 50 of relay OBS, winding of relay F and over the remainder of the two-wire line circuit previously described to the terminal of battery OB.

Assuming that there are four field stations connected to the line circuit, the four line re- It will not be aslays such as relay F of Fig. 3A are positioned to the left. Relay IS'I (and similar relays at the other stations) is positioned to the left by means of a circuit extending from (CN), winding of relay IST conductor 2!, front contact 29I of relay IV back contacts 292, 298, 294 and 295 of relays 2V 3V 4V and 5V respectively, conductor 290, front contact 28I of relay L0 front contact 280 of relay SA and contact 296 of relay F in its left hand position, to (B).

Relay PC is positioned to the right during the second on? period by means of a circuit which extends from (B-|), code jumper 33 (Fig. 2A), front contact 65 of relay CD conductor I 02, front contact 85 of relay 2V and over the remainder of the previously described circuit to the winding of relay PC. With relay PC actuated to the right, the line circuit is energized with a potential because the terminal of battery OB is now connected by way of contact 2I of relay PC in its right hand dotted position, back contact 58 of relay OBS and winding of relay F, to line conductor I2.

With the line relays at the stations positioned to the right, a circuit is closed for positioning the station relays similar to relay 2ST of Fig. 313 to the right by meansof a circuit similar to that extending from (CN), winding of relay 2ST conductor 202, front contact 292 of relay 2V and over the remainder of the previously described circuit to contact 296 of relay F now in its right hand dotted position, to (B+).

The station relays similar to relay IST at the four stations will be positioned to the left and the station relays similar to relay 2ST at the four stations will be positioned to the right.

During the third off period, relay 3V is picked up to disconnect at its back contact I85 the energized stick conductor E83 from conductor I81. At all of the stations except that one with code jumper 2H! connected as shown in Fig. 313, this opening of back contact I85 deenergizes the stick circuit of the lock-out relays and they are dropped. At the particular station illustrated, however, relay L0 throughout the remainder of the cycle by means of a circuit extending from front contact I82 of relay SA conductor I83, contact 2I2 of relay IST in its left hand dotted position, contact 2 of relay 2ST in its right hand position, code jumper 2I0, conductor I81, front contact I88 of relay SA front contact I98 and upper winding of relay L0 to With four stations selectable with combinations of two impulses, it will be obvious that in addition to the station illustrated which responds to code combination the other three respond to combinations and For example, at the station where code jumper H3 is connected to conductor I81, the code combination is and the lockout relay is maintained energized after the third step due to the circuit being completed from on stick conductor I83, by way of contacts 2M and 2| 5 of relays IST and 2ST respectively in their right hand positions and code jumper 2I3 to conductor I81. At the station where code jumper 2I6 is connected to conductor I81, the code combination for selecting this station is which requires that relays IS'I and 2ST be in their right and left hand positions respectively to complete the above described circuit for sticking the look-out relay similar to relay L0 At the station where code jumper 2I1 is connected to conductor I81, the combination which positions the station relays similar to lST and 2ST to the left completes an energizing stick circuit for the lock-out relay.

After the station is selected, the switch machine SM is controlled by the switch machine relay SMR as determined by the position of the switch machine lever SML. To actuate the switch machine to its reverse locked position as determined by relay SMR actuating its contact I84 to the left, requires that the line circuit be energized with a potential for positioning the line relays to theleft. The switch machine lever SML in its left hand dotted position completes a circuit for actuating the contacts of relay PC to the left which extends from (CN), winding of relay PC, conductor 95, back contacts 89 and 88 of relays 5V and 4V respectively, front contact 81 of relay 3V, conductor I03, front con Relay PC positioned to the left energizes the line circuit with a potential which positions relay F to the left to actuate relay SMR to the left over a circuit extending from (CN) ,winding of relay SMR conductor 203, front contact'293 of relay 3V back contacts 294 and 295 of relays 4V and 5V respectively, conductor 290, front contact 281 of relay L0 front contact 280 or is maintained energized relay SA and contact 296 of relay F in its left hand position, to (B). RelaySMR closes circuit from contact I84 in itsleft hand dotted position and the reverse winding of the switch machine motor SM to It is ob- Vious that the above conditions will be reversed, with lever SML in its right hand position, withthe result that the motor will be energized by way of contact I8 of relay SMR in its right hand position to energize its normal operating winding.

It is believed that the above example is sufiioient to indicate how other relays such as relays 8G and DR at the field station are positioned as determined by the position of a lever such as SGL of Fig. 2A and that these relays may actuate signals in any approved manner by means of their contacts in different positions.

Relays such as SMR SG and DR at those field stations not selected during the cycle are not energized, because conductor similar to 2951 at these other stations'is open at contacts similar to 28I of the deenergized lock-out relays. After the third step at these other stations, which results in the dropping of the look-out relays, the stepping operation is discontinued because the pick-up circuit of the stepping relays including conductors similar to 259 is open at front contacts similar to 251 of the look-out relays at these other stations.

Automatic start-When a change in condition occurs at a field station, change relay CH is dropped. This may be due to the entrance of a train into a detector track section, which deenergizes relay T for in turn closing a circuit from back contact I62 of relay T and winding of relay TR to Relay TR v picks up and closes a stick circuit for itself extending from back contact I53 of relay 5V and back contact I55 of relay S front contact I64 and winding of relay TR to It is obvious that the stick circuit remains efiective until relay 5V is picked up at the end of the cycle with its associated S relay also picked up. This latter relay will be picked up at the station which obtains access to the communication line. Another relay similar to relay TR at some other station is stuck up to store the change in condition, until the particular station with which this relay is associated obtains access to the communication circuit and relays similar to S and 5V are up at such station.

A change in condition at the field station may be brought about as a result of relay WP being momentarily deenergized as the switch machine is moved from its normal locked position to its reverse locked position, as a result of the control cycle previously discussed. In any event, the stick circuit of relay CH is interrupted at some contact, such as I55 of relay WP allowing relay CH to drop and close a circuit for picking up relay CI-IP extending from back contact I 82 of relay SA back contact I8I of relay FP front contact I of relay L0 winding of relay CHP conductor I59 and back contact 51 of relay CH to Relay CI-IP closes a circuit for picking up relay P which extends from front contact I6I of relay CI-IP and winding of relay P to This marks the end of the normal period (line relays in their left hand position) and the beginning of the initiating period, by de-energizing the line circuit at back contact 45 of relay P Reother stations are dropped to their neutral positions. Relay L0 in the control office is now dropped because its energizing circuits are opened at contacts 61 and 55 of relay F in its neutral position. Relay L0 is not picked up during this cycle because relay SA opens its back contact 51 before relay F is again actuated -to the left to close its contact 55.

Relay LO at the illustrated field station (as well as the other lock-out relays at all other stations) is now dropped because its energizing circuit is open at contacts I19 and HI of relay F in their neutral positions. The lock-out relays at all stations remain down during this cycle.

Conductor I86 leading to the: upper winding of relay F138 and contacts I92 and I93 of relays LOP and L0 respectively are only used at the end field station, but in order to indicate how relay FBS at the end field station is picked up at the start of an indication cycle, this conductor and these contacts have been shown in association with Fig. 3A. It will be understood that contacts similar to I92 and I93 are on corresponding relays at the end field station only. Relay FBS is picked up by means of a circuit similar to that extending from back contact I94 of relay SA back contact I93 of relay L0 front contact I92 of relay LOP and upper winding of relay PBS, to

Since relay P is up, conductor I2 extending from this field station toward the control oflice is open, but a circuit is effective to energize the line at this calling field station in series with any other station or stations toward the end of the line, as well as the end station. This circuit extends from the terminal of battery FB (see Fig. 1) front contact 32 of relay FBS back contact 30 of relay P0 conductor 29, back contact 21 of relay PC resistance R front contact I95 of relay CHP upper winding of relay S front contact 45 .of relay P winding of relay F back contact M of relay P0 conductor 22, back contact 49 of relay P winding of relay F back contact 36 of relay P0 and front contact 34 of relay FBS to the terminal of battery FB.

The current fiow in this circuit is of such a direction that relay F and other similar line relays farther out the line, are positioned to the right and relay S at this particular calling station is picked up. The dropping of relay L0 above described, opens the circuit of relay CHP at front contact I69, but before relay CHP has time to drop, a substitute circuit is closed which extends from contact Ill of relay F in its right hand dotted position, back contact I13 of relay SA back contact I19 of relay L0 front contact I11 of relay CHP back contact I69 of relay L0 winding of relay CHP conductor I59 and back contact I51 of relay CH to Relay F closes a circuit for picking up relay FP which extends from contact I19 of relay F in its right hand dotted position and winding of relay FP to Relay FP closes a circuit for picking up relay SA which extends from front contact I16 of relay FP and winding of relay SA to Relay SA opens the above described energizing circuit for relay CH]? at back contact I13 causing the release of relay CHP Even though relay CH is dropped as a result of another start condition, relay CHP cannot be picked up until the system goes into the normal condition because of the open cir-. cuit at front contact I 69 of relay L0 This also applies to other field stations, that is, a change resulting in the dropping of a relay similar to relay CH cannot pick up the change repeating relay similar to relay CI-IP because the look-out relays at all these other stations are down. Because of this condition, the system will function to transmit all the waiting controls in the control office before a relay such as relay CHP can be picked up. This is because as long as there are stored controls to be transmitted the system does not go into its normal condition for picking up the look-out relays, this being discussed in detail in connection with stored ofiice start conditions.

The picking up of relay 8A reenergizes relay CH over a circuit extending from front contact I82 of relay SA conductor I63, back contact 268 of relay IV conductor I15, front contact I66 of relay CHP front contact I61 of relay S conductor I68 and lower winding of relay CH to Relay CH of course will be stuck up until some change in condition takes place to interrupt the stick circuit through its upper winding.

The picking up of relay SA also opens the circuit of relay LOP (including its front contact I69) at back contact I94 of relay SA which causes the release of relay LOP and it remains down throughout the remainder of this cycle. The picking up of the relay similar to relay SA at the end field station closes a circuit for sticking relay FBSfi, which is similar to that extending from front contact I94 of relay SA conductor I18, front contact I99 and lower winding of relay FBS to contact I94 is of the make-before-break type so that this stick circuit is closed before the pickup circuit through the upper winding of relay F138 is interrupted. Relay SA closes a stick circuit for relay S extending from front contact I94 of relay SA front contact I91 and lower winding of relay S to Since these stick circuits are maintained throughout this cycle, relays S and PBS remain up during the cycle.

During the initiating period, relays PC in the control ofiice is normally positioned to the left over the previously described circuit which extends from the winding of relay PC, to (B), through front contacts 11 and 19 of relays L0 and LOP respectively. When relay L0 is dropped during the initiating period, the potential is shifted from (B) to (B+) at back contact 11 of relay LO which positions relay PC to the right. When relay SAP is picked up during the initiating period (as will be later explained), relay LOP is dropped because its energizing circuit is opened at back contact 66 of relay SAP. (B) potential is then applied through back contact 19 of relay LOP to the winding of relay PC so that this latter relay is positioned to the left in preparation for the next control cycle. The positioning of contacts 2| and 53 to the left after the release of relay LOP is ineffective, because relay OBS will bepicked up to interrupt the circuit from battery OB through back contacts24 and 50 as will be later described.

Referring to the field station circuits, the dropping of relay CHP previously explained opens the circuit of relay P at front contact I6I, which results in the release of relay P The line circuit from the calling station back to the control office is now energized by batteries OB and F3 in series. This energizing circuit may be traced from the terminal of battery FB (see Fig. 1), front contact 32 of relay FBS,

It will be noted that contact 2'! of relay P conductor I0, back contact 24 of relay OBS, contact 53 of relay PC in its right hand dotted position (this happens before relay LOP is dropped to shift relay PC to the left), terminal of battery OB, terminal of battery OB, contact 2| of relay PC in its right hand dotted position, back contact 50 of relay OBS, winding of relay F, front contact 4'! of relay EP, conductor I2, back contact 45 of relay P winding of relay F back contact M of relay P0 conductor 22, back contact 49 of relay P winding of relay F back contact 36 of relay P0 and front contact 34 of relay FBS to the terminal of battery FB It will be understood that this circuit also includes the line relays at all other stations.

Line relay F (and similar relays farther out the line) remain in their right hand positions and the other line relays (in the line towards the control oflice) including relay F in the control oflice, are actuated to their right hand positions. The previously described circuit is now closed for picking up relay IFP. Relays 2FP, SA, and SAP now pick up as described in connection with the initiating period of the control cycle, after which relay VP picks up and causes the release of relays E and EP in turn, all of which has been described in connection with the initiating period of the control cycle.

The dropping of relays E and EP deenergizes the line by opening front contacts 31 and 41. Relay OBS is now picked up by means of a circuit extending from front contact 68 of 0 relay SA, winding of relay OBS, back contact 18 of relay EP, front contact I6 of relay LOP and back contact ID of relay L0, to Relay OBS completes a stick circuit for itself which is effective during the remainder of this cycle and which extends from front contact 68 of relay SA, winding and front contact 82 of relay OBS,

The system now steps through the cycle and the line is impulsed by means of relays E and EP in the same manner previously described in connection with the control cycle with the following exceptions:Relay L0 in the control office is down and relay OBS is up. Relay EPT is conditioned to record indication code combinations as will be later explained. The lock-out relays at all stations are down and relay S at the calling station only is up. Relay FBS at the end station is up and relays P and PC at the calling station are conditioned as determined by the indication code to be transmitted. The length of each on period is variable in a manner to be later explained.

' Registration of the field station .-With jumpers I98 and I99 in the positions shown in Fig. 3B, the illustrated station will be registered in the control office during the first step of the indication cycle. It will be assumed that the system steps through the cycle in the previously described manner. With jumper I98 in the position shown, relay PC is not picked up: during the first off period, which results in the line circuit being energized with potential during the following ,first on period. This is due to the fact that the above described circuit from battery FB is through back contacts 2'! and II of relay PC and is in the proper direction to position all the line relays to the right. It will be understood that battery OB is excluded from the above described circuit when relay OBS picks up and closes its front contacts 24 and 59 to complete the energizlng circuit for the line from battery FB alone.

spectively, front contact II4 of relay IV, conductor I3I and upper winding of relay IPT, to (B-). Relay IPT closes a stick circuit for itself extending from front contact 68 of relay SA,

conductor 98, front contact I39 and lower Winding of relay IPT, to

In the event that a particular station is transmitting which has: its jumper I98 connected in its alternate position leading to then relay P0 is picked up during the first off period over a circuit extending from jumper I98, conductor 23I, front contact 200 of relay IV back contacts 206, 201, 208 and 209 of relays 2V 3V 4V and 5V respectively, conductor I9I, winding of relay P0 and front contact 2I8 of relay S to With relay P0 up, the connection of battery F3 to line conductors I0 and I2 is reversed which is effective to actuate relay F to the left. This closes a circuit from (B) at contact 96 of relay F in its left hand position to the upper winding of relay IPT and since the same potential is applied to both terminals of this winding, relay IPT remains down.

The above example illustrates the manner in which a choice of two polar indications are obtained during one step to condition a pilot relay by picking it up or leaving it down. Although these polar impulses are effective to position the line relays at all stations, they are not repeated at these stations because all lock-out relays are down and front contacts similar to 28I are open.

The system is also arranged to transmit an additional choice of. two conditions during each step by means of long and short energized conditions of the line. More specifically, during each step of an indication cycle, the line circuit may be energized for a comparatively long interval due to the control office opening the line circuit to mark the end'cf the on period. The field station may open the line circuit before it would otherwisebe opened in the control oflice, to mark the end of the on period in a comparatively shorter length of time than when this on period is terminated in the control oflice. These two conditions are determined at the field station in accordance with whether conductors 231 and 238 are deenergized during the.on period for providing a normally long on, or energized during the on period to provide an abnormally short on.

When the system is advanced'from the first off period into the first on period by relay E in the control office picking up to energize the line, a circuit is closed for picking up relay EP'I which extends from front contact 23 of relay OBS,winding of relay EPT and front contact I09 of relay E, to The line relays and the line repeating relays in the control ofiice and at the field station are picked up during this on period in the manner previously described. Relay VP is picked up and relay VP is dropped during the first on period as previously explained. When relay VP picks up, is applied to conductor 231 at front contact 239 of relay VP and with jumper I99 in the position indicated in Fig. 3B, this is ineffective since the circuit is open at this point. This results in relay P remaining down during this on period so that the line on period.

circuit is not opened at the field station but remains closed until opened in the control oflice.

- When relay VP in the control oflice drops, impulsing relay E is released as above described, but relay EP does not drop at this time because of a stick circuit extending from contact 55 of relay F in either its right or left hand position, front contact I4 of relay EPT, front contact I3 and lower winding of relay EP, to

The dropping of relay E opens the circuit of relay EPT at front contact I09 and after a predetermined interval of ..time, relay EPT drops and opens the above described stick, circuit for relay EP at contact I4. Relay EP now drops and the line is deenergized to mark the end of the first Relays F, IFP, and 2FP now drop in sequence and during the interval after relay 2PT drops and until relay 2F'P is dropped, the executing circuit for the long on is completed. This circuit extends from (3-), back contact II of relay EPT, front contact 9 of relay'2FP, front contact 8 of relay OBS, conductor I, back contacts H5, H6, H! and H8 of relays 5V, 4V, 3V, and 2V respectively, front contact H9 of relay IV, conductor I2I and upper winding of relay 2PT, to (B-). Since both terminals of this winding of relay 2PT are connected to (B-), the relay remains down to register the fact that the call ing station is one Where jumper I99 is not connected to conductor 231.

In the event that the calling field station is one with its jumper I99 connected to jumper 231, then when relay VP picks up and closes its front contact 239 as above described, the circuit is extended from at this contact through jumper I99, conductor 22I, front contact 230 of relay IV back contacts 229, 228, 221, and 226 of relays 2V 3V 4V and 5V respectively, conductor 298, front contact 2I9 of relay S front contact 220 of relay FP and winding of relay P to Therefore, relay P picks up and opens the line circuit as soon as relay VP shifts at the calling station.

Relay EPT in the control oifice is of course picked up at the start of the on period as before and when relay P opens the line circuit, relays F, IFP, and 2FP in the control oflice are dropped. Since the line is deenergized earlier than during'the alternate condition above described, relay F is dropped to its neutral position to close a circuit from (3+) contact I00 of relay F in its deenergized position, front contact H of relay EPT, front contact 9 of relay 2FP, front contact 8 of relay OBS, conductor I and over the remainder of the above described circuit to the upper winding of relay 2PT. Relay 2PT is picked up this time because (3+) is applied to the right hand terminal of its upper winding and it is stuck up over an obvious stick circuit including its front contact I20.

Relay EP is dropped as soon as relay F is restored to its neutral position to open its contact 55. It will be noted that the upper winding of relay EP is deenergized at this time because relays OBS and IFP are picked up. As soon as the half step relay VP is shifted, relay E is dropped to maintain the circuit of the upper winding of relay EP open until the start of the next on period. Relay EPT does not drop during this condition after relay E drops and opens its front contact I09, because of a stick circuit extending from back contact I26 of relay EP, front contact I21 of relay EPT, winding ofrelay EPT and front contact 23 of relay OBS, to

rxThe above example indicates how a station sends a message to the control ofiice which re cords the fact whether or not this station has its code jumper I99 in connection with bus wire 231, by picking up pilot relay 2PT if this jumper is so connected and leaving pilot relay 2PT down if the jumper is not so connected.

The above two examples indicate how a choice of four indications is obtained during a single step for registering calling stations in the control oflice. With jumpers I98 and I99 in the positions shown in Fig. 3B, relay IPT is up and relay 2PT is down when the system is advanced into the second off period, which occurs after the station registration code has been transmitted. A

circuit is now closed for picking up station relay ST which extends from front contact 23 of relay OBS, conductor 6, front contact I28 of relay 2V, conductor I29, back contact I39 of relay 2PT, front contact I538 of relay IPT and winding of relay ST, to Relay ST remains energized until the end of the cycle.

Since the pilot relays IPT and 2PT can be positioned in any one of four combinations during one step of the cycle by the four different possible combinationconnections of jumpers I98 and I99,

any one of four field stations may register itself in the control office during one step. The four different combinations of the two jumpers are; first, I98 connected to and I99 connected to conductor 23'! resulting in relay IPT remaining down and relay 2PT being picked up; second, with jumper I98 connected to and jumper I99 disconnected from wire 231, relay IPTremains down and relay 2PT remains down; third, jumper I98 disconnected from and jumper I99 connected to wire 231 results in relay IPT being picked up and relay 2PT being picked up; fourth,

jumper I98 disconnected from and jumper I99 disconnected from wire 2331, relay IPT is picked up and relay 2PT remains down.

With these four pilot relay combinations, four station relays such as relay ST can be selectively picked up to register any one of four calling stations. With two additional pilot relays operated in the same manner during the second step, sixteen station relays similar to relay ST can be selectively picked up to register any one of sixteen calling stations in the control oiiice.

Indications from registered station.--After the calling station registers itself in the control office, the particular indications from this station are transmitted during additional steps of the system. When the station is registered during the firststep, the first indication condition from the station is executed during the second on period. Assuming that relay W]? of Fig. 3B actuated its polar contact 249 to its left hand dotted position as a result of the previously described control cycle, this position of contact 240 indicates that the switch machine has been moved to its reverse locked position. Itwill also be assumed that the detector track section illustrated is occupied and as a result, relay TB is picked up.

When the system advances into the second off tact 24I of relay WP contact 249 of relay WP in its left hand dotted position, conductor 232, front contact 296 of relay 2V and over the remainder of the previously described circuit through the winding of relay PC to at front The picking up of re-- contact 2I8 of relay S F13 through front contact 4| of relay PC and front contact 3d of relay FBS Relay F in the control oifice in its left hand position closes a circuit for actuating the No. 1 indication receiving relay IIR to its right hand 5 position, which circuit extends from (B), contact 9B of relay F in its left hand position, front contact E9 of relay SA, front contact 9'! of relay OBS, back contacts H9, III, and H2 of relays 5V @V and 3V respectively, front contact H3 of relay 2V, conductor 32, front contact I36 of relay ST and winding of relay IIR, to (CN) When the system advances into the third off period, the picking up of relay 3V extends the circuit from relay PC by way of front contact 5 297 of relay 9V and conductor 233 to polar contact 249 of relay WP in its right hand position. Since it was assumed that relay WP has its contact 249 actuated to the left hand dotted position, the energizing circuit for relay PC is incomplete 30 during the third on period, so that the line is energized through back contacts 21 and II of relay PC to position the line relays to the right.

Relay F closes a circuit from (B+) at contact 98 in its right hand dotted position through front 5 contact I9 of relay SA, front contact 91 of relay OBS, back contacts III! and III of relays 5V and 4V respectively, front contact H2 of relay 3V, conductor I33, front contact I31 of relay ST and winding of relay HR, to (ON). This circuit is 40 effective to position relay HR to the left.

With relay IIR positioned to the right and relay 21R positioned to the left, as a result of relay WP being positioned to the left to indicate a reverse locked condition of the switch machine, a

45 circuit is completed for lighting lamp R to indicate this condition. This circuit extends from contact Mi of relay IIR in its right hand position, contact I42 of relay HR in its left hand position and lamp R, to

50 In the event that polar contact 249 of relay WP is in its right hand position due to the switch machine being normally locked, then the above described circuit during the second off period is ineffective to pick up relay PC This 55 results in the line circuit being energized with current in the opposite direction to that above explained, so that relay F actuates its contact 96 to the right and relay IIR. is positioned to the left, because (B+) from contact 96 in its right 60 hand dotted position is connected to the winding of relay 51R over the above described circuit.

The alternate condition of relay WP at the third step, that is contact 240 in its right hand position, is effective to pick up relay PC which 65 positions relay F to the left for closing the above described circuit from (B) at contact 96 of relay F to the winding of relay 2IR, which in turn positions relay 21R to the right.

Relay IIR positioned to the left and relay 21R 70 positioned to the right closes a circuit from contact I42 in its right hand position and contact MI in its left hand position, to lamp N,

which lights this lamp as an indication that the switch machine is in the normal locked position.

75 In the event that contact 24I of relay WP is in 2FP, front contact 8 of relay OBS, conductor 1 its deenergizedposition, then there is no energizing circuit for relay PC on either the second or third steps so thatthe line conductor is energized in such a direction that relay F in the control ofiice is positioned to the right on both i the first and second steps. (B+) at contact 96 in its right hand dotted position is then connected to both indication receiving relays IIR and 21R in turn, to position both of these relays to the left. This results in both lamps N and R remaining relatively dark as an indication that the switch machine is in its unlocked or midstroke position.

As typical of the manner in which the short and long on periods may be used to transmit indications, it will be assumed that relay TR is picked up. When relay VP drops during the second on period, a circuit is closed for picking up relay P which extends from back contact 239 of relay VP conductor 238, front contact 236 of relay 'IR conductor 222, front contact 229 of relay 2V and over the remainder of the previously described circuit to the winding of relay P Relay P picks up and deenergizes the line circuit at its back contact 45. This marks the end of the second on period, this energized period of the. line being comparatively short due to the field station opening the line circuit before relays E and EP in the control ofiice drop to open the line.

Relays F, IFP, and 2FP now drop. Since relay VP is picked up during the second on period, relays E and EP are dropped. Relay EPT (picked up when relay E was picked up to close its front contact IE9) is now stuck up even though front contact I09 is opened, by means of a circuit to through front contact I21 of relayEPT and back contact I25 of relay EP.

Relay F in its neutral position closes .a circuit from (B+), contact I99, front-contact II of rel-ay EPT, front contact 9 of relay ZEP, front contact 8 of relay OBS, conductor 1, back contacts H5, H6 and Ill of relays 5V, 4V, and 3V respectively, front contact N9 of relay 2V, conductor I22, front contact I43 of relay ST and winding of relay 31R, to (CN). This actuates contact I46 of relay 31R to the left hand dotted position,'which lights lamp OS as an indication that the detector track section of Fig. 3B is occupied.

In'the event that relay TB. is down, then the above described circuit for picking up relay P is not completed, which results in the line remaining energized for a comparatively long interval until it is opened in the control oflice. Under this condition, relay E is dropped during the second"on period when relay VP picks up as previously described. Relay EP is not dropped under this condition until after relay EPT drops because of the stick circuit extending fromv contact 55 of relay F in either its right or left hand position, front contact Id of relay EPT, front contact I3 and lower Winding of relay EP, to

When relay EPT drops, the above described stick circuit of relay EP is opened allowing this latter relay to be deenergized to mark the end of the second on period by opening the line circuit. Relays F, IFP, and 2F? now drop in sequence and during the interval after the dropping of relay EPT and until the dropping of relay ZFP, a circuit is closed from (B), back contact I! of relay EPT, front contact 9 of relay back contacts II5, H6, and II! of relays 5V, Av 

